Football.London understands Goncalo Cardoso has been handed a five-year contract to complete his move from Boavista to London for €3m.
The 18-year-old defender has undergone and passed a medical on Monday and the club is putting the finishing touches to his deal and the official announcement could come later today (Tuesday).
Cardoso only made his debut for Boavista last October as a 17-year-old but went on to make 15 appearances in the Portuguese top flight in the remainder of the season.
The Hammers have fought off competition from Portuguese giants Benfica, as well as interest from Italy, to secure the signature of the highly-rated centre back.
He will join West Ham as a fourth choice central defender behind Issa Diop, Fabian Balbuena and Angelo Ogbonna but is expected to challenge for first team regular honours in th near future. What that means for Hammers defender Winston Reid remains to be seen.
The club has no plans to throw him into the U23s exclusively at Chadwell Heath though he could turn out for the youngsters in PL2 initially to get up to speed with the English game.
Other Portuguese youngsters who have joined the club - Domingos Quina, Xande Silva and Mesaque Dju - have gone to Chadwell Heath first of all before aiming for a step up to the first team.
Manuel Pellegrini now has the U23s training alongside the first team on the training pitches at Rush Green but the two entities are still kept separate, with the younger players returning to Chadwell Heath after training has been concluded.
